In various types of electrically operated apparatus in which a housing or other metallic structure is provided and can be at an electrical potential different from that of another part of the apparatus, it is a common practice to provide an insulating current feed-through device or assembly which can be provided with a feeder conductor designed to prevent electrical bridging between the housing and the conductor which can be connected to an internal electrical structure.
In, for example, an electrostatic precipitator, a metal housing generally encloses a space containing corona discharge electrodes and dust-collector electrodes disposed above a bin in which the dust is collected upon rapping of at least the collector electrodes.
The dust-laden gas passes through this space and the dust particles become electrically charged to a potential opposite that of the collector electrodes, thereby establishing electrostatic attraction forces between the collector electrodes and the dust particles enabling the dust particles to accumulate on the collector electrodes.
The housing and the collector electrodes may be one electrical potential, e.g. ground, while the corona discharge electrodes may be supplied with the opposite electrical potential, such as thousands of volts, with the conductor and a feed-through insulating assembly in the wall of the housing. The housing thus is provided with a hole or opening traversed by the conductor and insulated therefrom by the insulating members of the feed-through assembly.
A feed-through device for this purpose is known, for instance, from Opened German Specification (Offenlegungsschrift) DE-OS No. 2,556,546 and comprises a tubular element, which encloses the electrical conductor and has a flaring conical portion toward the interior of the electrostatic precipitator and is provided on the outside with screw threads for fixation.
That element is surrounded by a sleeve, which is made of elastic insulating material and has also a flaring conical inner portion and is fitted into a suitably shaped feed-through opening in the wall. For assembly, the sleeve made of elastic insulating material and the tubular element are clamped to the wall by means of the flaring conical portions.
The flaring conical portion of the tubular element is larger than the smallest cross-section of the opening in the wall so that even when the sleeve made of elastic insulating material has been damaged the tubular element cannot be thrown out of the wall under the internal superatmospheric pressure. As a result, there will be no leak in the electrostatic precipitator even when the insulator has been damaged.
A disadvantage of devices of this type resides in that it can be used only at temperatures up to an upper limit because elastic insulating materials which can be used at higher temperature have not been available thus far.